1. Field of the Invention
The present invention relates to a measuring apparatus of a location error (parallel translation errors ΔX, ΔY, and ΔZ in X, Y, and Z axial directions, and rotary direction errors ΔA, ΔB, and ΔC around X-, Y-, and Z-axes) of a work installed on a table in a machine tool.
2. Description of the Related Art
In a machine tool, when a work is installed and fixed on a table, it may be installed apart from a position which should be installed, and a location error arises. That is, in a machine tool controlled by a numerical controller, displacement arises between a position of the work supposed in a machining program, and a position of the work installed on the table. This location error is composed of parallel translation errors ΔX, ΔY, and ΔZ in X, Y, and Z axial directions, which are mutually orthogonal straight line axes, and rotary direction errors ΔA, ΔB, and ΔC around the X-, Y-, and Z-axes.
A method and an apparatus for performing correction and working with a numerical controller without correcting a location of a work and modifying a machining program by setting this location error (parallel translation errors ΔX, ΔY, and ΔZ in X, Y, and Z axial directions, and rotary direction errors ΔA, ΔB, and ΔC around the X-, Y-, and Z-axes) in a numerical controller beforehand have been already provided (Japanese Patent Application Laid-Open No. 7-299697).
In addition, a method of finding a diameter of a touch probe and an amount of an installation position displacement of the touch probe when measuring size and end face positions of a work with the touch probe, and correcting measurement positions is known (refer to Japanese Patent Application Laid-Open No. 2-64404). In particular, regarding a work having two faces forming a square corner section, this Japanese Patent Application Laid-Open No. 2-64404 discloses a method of obtaining an intersection coordinate Pa (xa, ya) of a square corner section of a work, in addition to an inclination (θ) of the work, by measuring two points in one face of the square corner section and one point in the other face of the square corner section. When applying this method described in Japanese Patent Application Laid-Open No. 2-64404, it is possible to obtain a location error of a work with a two-dimensional shape. That is, let an intersection coordinate of a corner part of an original work be PO (xo, yo), andΔx=xa−xoΔY=ya−yoΔc=θthen, it is possible to obtain errors ΔX and ΔY in the X-Y plane, and a rotation error ΔC around the Z-axis which is orthogonal to the X-Y plane, as a location error of the work with a two-dimensional shape.
Although measuring a position of a work with a sensor is described in the Japanese Patent Application Laid-Open No. 7-299697 mentioned above, a measuring method is not described at all.
In addition, the measuring method described in the Japanese Patent Application Laid-Open No. 2-64404 only obtains an error on two dimensions, but cannot obtain a parallel translation error ΔZ in a Z axial direction and the rotary direction errors ΔA and ΔB around the X-axis and Y-axis, in addition to parallel translation errors ΔX and ΔY in X-axis and Y-axis directions and a rotary direction error ΔC around the Z-axis.
A work usually has a three-dimensional shape, and as shown in FIG. 14, a location error of a three-dimensional work appears as parallel translation errors ΔX, ΔY, and ΔZ in X, Y, and Z axial directions, and rotary direction errors ΔA, ΔB, and ΔC around the X-, Y-, and Z-axes.
In FIG. 14, reference numeral 1 denotes a work installed in a position where the work should be installed originally, reference numeral 1′ denotes an actually installed work, and let reference coordinates in which the work should be installed originally, be a coordinate system (X, Y, Z) (reference numeral O denotes an origin), and let a coordinate system, in which the work is actually installed and which has a location error, be a coordinate system (X′, Y′, Z′) (reference numeral O′ denotes an origin). In this case, a vector [OO′] is a parallel translation error (ΔX, ΔY, ΔZ), and, the (X, Y, Z) coordinate system transfers to a coordinate system (X′, Y′, Z′) with rotation error ΔA around the X-axis, a rotation error ΔB around the Y-axis, and a rotation error ΔC around the Z-axis added, and those ΔA, ΔB, and ΔC constitute rotary direction errors (ΔA, ΔB, ΔC) around respective axes.